This invention relates to liquid phase epitaxy of compound semiconductor material. More particularly, it relates to growth of a plurality of different epitaxial layers on a plurality of semiconductor wafers in a single temperature cycle.
Liquid phase epitaxial growth for the fabrication of devices useful in optical communications and other applications is well known. Techniques are available, as disclosed in U.S. Pat. No. 3,853,643 to H. W. Verleur for liquid phase growth of a single epitaxial layer on a plurality of wafers in a single heating cycle. It is also known to grow a succession of different epitaxial layers on a single wafer. Such a procedure is shown in U.S. Pat. No. 4,028,128 to Y. Horikoshi.
In connection with processes of liquid phase epitaxial growth, the use of a predetermined two-phase melt assures that the nutrient solution has the identical degree of saturation desired for the growth of a particular layer at a predetermined growth temperature. Use of a two-phase melt involves the presence of some solids in the nutrient solution to assure excess saturating sources of certain constituents. It is significant that when one layer of a multiple-layered structure is being deposited in a predetermined growth cycle, and the rest of the melts undergo cooling, this two-phase system assures maintenance of the same degree of saturation as each of the subsequent layers is deposited. Because of this, it is important that during the growth process the melt be continuous; that is, that those portions of the melt at the growth faces be in contact with and a part of the portion of the melt containing the saturating solids in order to maintain the same saturation conditions for growth. It is important also to maintain the separation of the several melts without intermixing to assure the desired composition of the individual layers.
Accordingly, an object of the invention is multi-slice, multi-layer liquid phase epitaxy process which enables fabrication of semiconductor devices on a batch basis having a plurality of layers in a single heating cycle.